This invention relates to an apparatus or a method for processing in a processing chamber a substrate sample such as a semiconductor wafer by using plasma formed in the processing chamber housed in a vacuum vessel.
In a plasma processing apparatus in which a sample such as a semiconductor wafer is mounted on a sample stage and the sample is processed with plasma formed over the sample, for example, there are two general processes: one is to remove the intended film existing over the sample surface with a chemical reaction taking place between the sample and the plasma, and the other is to deposit a new film over the surface of the sample. The former is called “etching process” while the latter is called “CVD (chemical vapor deposition)”. In such plasma processing procedures, process proceeds through chemical reactions between the sample and ions or active gases that are in the form of chemically active plasma. It is to be noted that the temperature of the sample greatly affects whether or not the chemical reaction mentioned above starts, whether or not the reaction product, in the form of gas generated as a result of the chemical reaction, is released from the sample surface (etching), or whether or not the reaction product deposits as solid on the sample surface (CVD).
When it is desired to etch such a sample whose reaction product has a low vapor pressure, it is necessary to keep low the pressure within the plasma processing chamber or to elevate the temperature of the sample so that the reaction product can be gasified and released from the sample surface. In practice, a certain degree of pressure must be maintained within the plasma processing chamber (not less than 0.1 Pa) and the temperature of the sample must be elevated sufficiently, so as to stabilize the plasma atmosphere in the plasma processing chamber.
In this way, it is necessary to control the temperature of the sample in accordance with desired processes. For this purpose, the temperature of the sample is usually adjusted to a desired value by controlling the temperature of the sample stage mentioned above. Conventional mechanisms for controlling the temperature of the sample stage include causing heat exchanging fluid, whose temperature is controlled, to flow through within the sample stage, or embedding a heater in the sample stage.
On the other hand, the temperature of the sample is controlled through the heat transfer between the sample and the sample stage. Therefore, in order to effectively perform the heat transfer between the sample and the surface of the sample stage facing the sample, the sample is electro-statically chucked to the upper surface of the sample stage and heat transfer gas such as helium is injected into the gap spaces between the lower surface of the sample and the upper surface of the sample stage. Further, much consideration has been given to the condition for the most effective electrostatic chucking and the area on the sample stage where the sample is to be electro-statically chucked since the control of the sample temperature is greatly affected by the efficiency of heat transfer.
JP-A-09-167794 is known to disclose such a conventional technique as described above. According to the disclosed technique, while a semiconductor wafer is fixed to the sample stage by means of multiple chucking electrodes working in a bipolar configuration, heat transfer gas is fed to control the temperature of the wafer; and while the sample is chucked onto the sample stage under the influence of the multiple chucking electrodes working in a mono-polar configuration, the wafer is processed.
In general, a substrate sample such as a semiconductor wafer is at room temperatures before it is subjected to plasma process, the sample is then mounted on a sample stage which was kept at a desired temperature, the sample is chucked onto the surface of the sample stage, and the temperature of the sample is controlled through heat exchange between the sample and the sample stage.
In case, for example, where a sample, kept at high temperatures of 200° C.˜300° C., is processed with plasma, the sample stage is always kept at high temperatures; the sample is mounted on the sample stage kept at high temperatures and then electro-statically chucked onto the sample stage; and the sample is heated with gas as heat transfer medium filled in gap spaces between the sample and the sample stage. When the temperature of the sample is elevated to a value suitable for plasma processing, plasma process will start.
In this case, the sample thermally expands while it is electro-statically chucked onto the sample stage. Accordingly, the lower surface of the sample and the upper surface of the sample stage are subjected to abrasion, so that fine particles (of contaminating material) are produced or the surface roughness of the lower surface of the sample and the upper surface of the sample stage is changed. This in turn changes the efficiency of heat transfer between the sample and the sample stage, leading to the degradation in the control of sample temperature. This adverse effect is not described in the above-mentioned related art technique.
The object of this invention is to provide a plasma processing apparatus or a plasma processing method, which can enjoy a high productivity by employing a technique that can suppress the production of fine particles and the abrasion of the upper surface of the sample stage.
The aforesaid object of this invention can be attained by a plasma processing apparatus including:
a processing room disposed in a vacuum vessel, within which plasma is generated in a depressurized state;
a sample stage located in a lower position in the processing room, over the top surface of which a sample to be processed with the plasma is mounted;
a dielectric film disposed on the top surface of the sample stage and serving as the sample mounting surface of the sample stage; and
a plurality of electrodes embedded in the dielectric film for chucking the sample to the dielectric film when supplied with electric power,
wherein a part of the sample is chucked by supplying electric power to at least one of the electrodes while the sample is mounted on the sample stage; the sample is heated up to a predetermined temperature; a larger part of the sample is chucked by supplying electric power to the other of the electrodes; and the processing of the sample using the plasma is initiated.
The aforesaid object of this invention can also be attained by a plasma processing method in which a sample to be processed is mounted on the sample mounting surface of a sample stage disposed in a processing room contained in a vacuum vessel, and the processing room is depressurized to generate plasma for processing the sample, wherein a part of the sample is electro-statically chucked to an electrostatic chucking electrode disposed beneath the central area of the sample, the sample is heated up to a predetermined temperature; the entire body of the sample is electro-statically chucked to the sample mounting surface, and the processing of the sample is initiated.